Submitted to: Magnetic Resonance in Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2002
Publication Date: 7/25/2002
Interpretive Summary: Except during periods of starvation, glucose is the primary source of energy for the activities of the brain. Electrical activity of regions of the brain depends on glucose as a source of energy, and the magnitude of neuronal activity has been correlated with the rate of glucose metabolism in the brain. It is therefore extremely important to be able to measure the erate of glucose metabolism in the brain. Existing methods for estimating the rate of cerebral metabolism, however, cannot accurately determine the rate in a time period of less than 30-40 minutes (even though the isotopic measurement itself may take only a few minutes) because they require sufficient time for the metabolism of the isotopically labeled substance that is administered. We report preliminary findings on a method for estimation of the rate of cerebral glucose metabolism over a period of ten minutes. We have tested this method in two groups of anesthetized rats: a control group and a group to which was administered an injection of bicuculline, a chemical that has been shown to increase the rate of cerebral glucose metabolism. Our measurement of glucose metabolism in the control group agrees with the value reported over 45 minutes using one of the other methods. As expected, the bicuculline-treated group had approximately three times the rate of glucose metabolism. After more testing and validation, this method should allow the investigation of rapid changes in cerebral metabolism following different stimuli (eating, loud sounds, bright lights, etc.) and will thereby increase our understanding of the mechanisms by which the brain allows us to understand our world.
Technical Abstract: Methods for estimation of the rate of cerebral utilization of glucose (CMRglc) typically measure metabolic activity during 40 minutes or longer subsequent to the administration of [13C]glucose, 2-[14C]-deoxyglucose or 2-[18F]-deoxyglucose. We report preliminary findings on estimation of CMRglc during periods of 10 minutes or less, using 2-[6-13C]deoxyglucose. Anesthetized rats were infused with [1-13C]glucose for 50 minutes and injected with 2-[6-13C]deoxyglucose (500 mg/kg). During the subsequent 9.6 minutes, the estimated value of CMRglc was 0.548 +/- 0.370 mumol/g/min (mean +/- SD, n=7), in agreement with values reported for anesthetized rats studied with the 2-[14C]-deoxyglucose method. In rats injected with bicuculline methiodide (a known stimulant of CMRglc), the value of CMRglc tended to increase to a value of 1.84 +/- 1.61 mumol/g/min (n=6, p=0.056). Cerebral glucose concentrations were higher in the bicuculline-treated group (25.01 +/- 5.64 mM vs 14.97 +/- 7.97 mM, p < 0.05).